1. Field of the Invention
This invention relates to a method of polishing electronic parts or like workpieces in the form of thin plates.
2. Description of the Prior Art
Recently, highly precisely machined thin plates of ceramics are extensively used as substrates of electronic parts. For example, alumina titanium carbide (Al.sub.2 2O.sub.3 /Tic) is used as a substrate of a thin film head of a computer, and the head requires very high accuracy such as a throat height of 1.5.+-.0.5 .mu.m, a flatness of 0.04 .mu.m and a surface roughness of 0.02 .mu.m.
FIGS. 8 to 10 illustrate a prior art method of polishing for the throat height. In this method, chips 10 cut to unit size are bonded to a work support disk 11 by adhesive 12 capable of being thermally softened as shown in FIG. 8, and they are polished in a manner as shown in FIG. 9.
FIG. 10 shows a block-like workpiece 1, which is cut into the chips 10. Reference numeral 14 designates dashed lines, along which the block 1 is cut into the chips 10, and numeral 15 designates a phantom line, up to which the block 1 is polished from the top. Designated at d.sub.1, d.sub.2, . . . are polishing margins of the block from the top thereof to the position of the phantom line 15. As is shown, the polishing margin varies (such as d.sub.2 &gt;d.sub.1) with the individual chips 10, which are cut from the elongate block 1, because of problems in the manufacture of the block 1 (dicing process of wafers).
Further, the adhesive 12 used to bond the chips 10 to the disk 11 fluctuates in thickness in the order of microns.
In FIG. 9, a large-size lapping disk 13 is rotated while supplying abrasive particles 3 from an abrasive feeder 4, and the work support disk 11 facing the abrasive feeder 13 is rotated. In this way, the chips 10 are polished with the abrasive 3 on the top surface of the lapping disk 13.
In the method of polishing shown in FIG. 9, the rotation of the lapping disk 13 is stopped for every several ten seconds, the work support disk 11 is removed from the lapping disk 13, the polishing status of the individual chips 10 is observed with a microscope, and chips which have been completely polished are removed.
FIG. 11 shows a different prior art method of polishing In this case, a sensor 17 for detecting a desired extent of polishing is provided at each of the opposite ends of block-like workpiece 1. This block-like workpiece 1 is directly bonded to the work support disk 11 and polished on the lapping disk 13 shown in FIG. 9. In this method, the machining is performed while on-line measuring the extent of polishing. (After polishing, the work is cut into the chips.)
The first-mentioned prior art method of polishing, however, involves a large number of steps and requires some manual operation and long time of operation. In the second-mentioned prior art method, since the thickness of the block-like workpiece varies locally, it is very difficult to mount the sensors at intended positions accurately. Thus, a considerable time is required for positioning, and the yield is inferior.